This article is about the road classification. For the road between Middlesbrough and Redcar named "Trunk Road", see A1085.

A Trunk road (or national road in the Republic of Ireland) is a road maintained by a national government body – as distinct from the great majority of roads, which are maintained by local Highway Authorities. Trunk roads are generally, therefore, the most important roads nationally; for example, most (though not all) British motorways are trunk roads.

An individually numbered road may be a trunk road for all, part, or none of its length. Equally, an individual trunk road may contain sections of several different numbered roads within its length.

The bodies responsible for the management and improvement of trunk or national roads within the United Kingdom and Ireland are:

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Early history of the term

According to the Oxford English Dictionary (OED), the first recorded use of the phrase trunk road was in 1822, in relation to the Grand Trunk Road in India, and over the next few decades it appears to have been used exclusively in this sense. The OED's first recorded use of the phrase in relation to the UK is from Tom Brown's Schooldays in 1861: "Englebourn lay on no trunk road."

At that time the phrase had no precise legal or technical meaning and it meant any main road used by long-distance traffic. It is still used in that sense by some people.

Hansard shows that the term was frequently used in Parliament in the 1850s in relation to India, but not until 1877 in relation to the UK. From then on, except for a spike in usage during the debates on the Development and Road Improvement Funds Act 1909, the term was not much used in Parliament until the mid-1920s, when it became commonplace.

Ireland

In the Republic of Ireland, the term National Road is preferred, the "national road network" being made up of

other National Primary Roads (bearing numbers in the range 1–50 and prefixed by "N")

National Secondary Roads (bearing numbers in the range 51–87)

Historically, the phrase "trunk road" in an Irish context referred to the main routes in the first Irish road numbering system, which were known as Trunk Roads and given the prefix letter of "T". These numbers were phased out in the 1970s, although there remain a few examples of old T-road signage dotted around the country.

United Kingdom

Trunk Roads in England and Wales came into being on 1 April 1937, and in Scotland on 16 May 1937, when the Trunk Roads Act 1936 came into force. The Ministry of Transport took direct control over the most important routes, though in an interesting quirk, roads within County Boroughs and the County of London were not trunked. Although the Scottish Office existed at the time, it initially had no responsibility for trunk roads.

The 1936 Act created 30 trunk roads totalling 4459 miles of road. As one trunk road was "Gretna - Stranraer - Glasgow - Stirling" and another was "Perth - Aberdeen - Inverness" it can be seen that a trunk road is not invariably the best route between its endpoints (though these were the only two such striking examples, and would perhaps have been better treated as two trunk roads each).

In 1946, a second Trunk Roads Act was passed, which created 71 new trunk roads between towns and gave trunk status to about 36 sections of road in County Boroughs and Large Burghs which would otherwise have formed gaps in trunk roads. However, no roads were trunked within the then County of London or within most of the largest cities. Overall the Act extended the trunk network by 3685 miles.

The 1946 Act also provided for roads to be added to or removed from the trunk network in future by statutory instrument without requiring a further Act of Parliament, and gave the Ministry further powers including those relating to junctions, bridges and the purchase of land around the road to prevent frontage development.

Early plans for a separate numbering system for trunk roads (see below) fizzled out, and trunk roads are generally known by their A road numbers. Most maps do not distinguish trunk roads from other Primary Routes. The trunk road network as it was at the relevant dates can be seen on SABRE Maps by clicking on "Historic OS Maps" followed by "1939 Ten Mile", "1946 Ten Mile" or "1956 Ten Mile".

In 1956, responsibility for trunk roads in Scotland was transferred from the Ministry of Transport to the Scottish Office. The Welsh Office was created in 1964 and its responsibilities from the start included trunk roads in Wales.

In 1999, with the creation of the Scottish Parliament and Welsh Assembly, responsibility for trunk roads in Scotland and Wales passed from the Scottish and Welsh Offices to the new Scottish and Welsh Ministers.

When a bypass is built on a trunk road, the section bypassed is "detrunked" (ceases to be a trunk road and becomes the responsibility of the local Highway Authority). From 1958, motorways began to be opened; the majority of sections of motorway also relieve a specific section of all-purpose trunk road and this is again usually detrunked.

Although the great majority of motorways are legally trunk roads, the term "trunk road" is often used as shorthand for "non-motorway trunk road" (or equivalently "all-purpose trunk road". The terms "trunk motorway" and "non-trunk motorway" are sometimes used.

Changes to the trunk road network can also result from a more general review. Thus in the 1950s the London-Penzance trunk road was rerouted from the A30 to the A303 over the full (then) 91-mile length of the latter, without any alteration to road numbers. Other major reroutings of trunk roads, such as between the Midlands and East Anglia and between Dundee and Aberdeen, have been accompanied by renumbering.

In the late 1990s a review of the trunk road network in England following the publication of A New Deal for Trunk Roads in England led to a decision, implemented over the next 10 years, to detrunk many trunk roads, most of which were less heavily trafficked and were (and are) still single carriageways. Today, the Trunk Road Network in England has been pared back to only the most important strategic routes, known as the Strategic Road Network (SRN), a high proportion of which are motorways or dual carriageways. In Wales and Scotland a higher proportion of A roads remain trunk roads; in rural mid-Wales most A roads are trunk roads.

In 2004 (in preparation for an expected system of elected regional assemblies which never materialised after an unfavourable result in a referendum in the north-east) the remaining trunk roads in England were further divided into "national" and "regional" ones (though all remained legally trunk roads). Subsequent events such as the recession and the 2010 general election appear to have reduced the relevance of this distinction.

Trunk Road Numbers

Each trunk road defined by the 1936 or 1946 Acts has a name, such as "the London-Edinburgh-Thurso trunk road".

A separate numbering system for trunk roads (using the prefix "T") was proposed. There were plans to show these numbers on signs. However this never happened, as A road numbers were starting to be signed well and used for navigation. Trunk road numbers were still being used internally in the Ministry of Transport in the early 1960s.

A road's trunk status is sometimes indicated by appending "(T)" to its A (or very rarely B) road number, as in "A34(T)". This usage may have originated with the Ordnance Survey, which used it on many of its maps between about 1950 and 2000; it has also been used in documents produced by local authorities and other bodies. It should not be used on signs, but incorrect signage has used it in some places.